The overall objective of this project is to use semen quality as a biomarker of effect on the male reproductive system resulting from occupational and environmental exposures. Occupational exposure to lead will be the focus of this study. The study design will be across sectional survey of approximately 100 men with known occupational exposure to lead and approximately 100 unexposed referent subjects of similar age. Blood and urine samples will be obtained to determine lead exposure. Acute lead exposure will be determined by blood lead and delta-aminolevulinic acid levels, and chronic lead exposure by urinary coproporphyrin excretion profiles. Demographic data, occupational and reproductive history, and the presence of potential confounding variables, such as alcohol use and existing disease states, will be obtained by questionnaire. Semen quality will be determined by traditional semen quality assays (sperm count, morphology and motility) and newly developed flow cytometric techniques (sperm chromatin structure assay (SCSA), mitochrondrial function, anf glutathione content). The effects of acute lead exposure on semen quality parameters will be assessed by comparing the measures of semen quality between subjects with high, moderate, low, and unexposed lead exposure. The epidemiologic utility of urinary coproporphyrin profiles as biomarkers of lead induced damage will be determined by relating porphyrin excretion patterns to blood concentrations of lead and I-aminolevulinic acid, and by comparing the measures of semen quality between subjects with hgh, moderate, low levels of chronic lead exposure. Standardized fertility ratios will be calculated for the study subjects classified by acute and chronic lead exposures (none, low, moderate, high) to estimate the fertility of lead exposed workers. This study will provide useful information on the reproductive consequences of occupational lead exposure, and will serve as a model for evaluating the effects of occupational and environmental exposures on male reproductive function.